1. Field of the Invention
The present invention relates to a latch needle for stitch forming textile machines. The latch needle includes a needle shank and a needle hook following the end of the shank. A latch slot is formed in the needle shank and extends in the longitudinal direction of the needle. A latch is also mounted on an axle in the latch slot at a location so as to be pivotal about a transversely extending pivot axis. The latch is provided on one end with a latch spoon which cooperates with the needle hook when the latch is in the closed position. The latch has an end portion which extends from the region of a latch blade or stem near the axle to the end facing away from the latch spoon. The needle shank includes a groove-like depression following the latch slot which extends toward the end facing away from the needle hook. One end of an elongate spring element is anchored in the groove-like depression while he other end of the spring element projects into the latch slot. When the needle latch is in the closed position the spring element passes over an associated contact face at one end of the latch stem. The spring element is positioned and the end of the latch stem is shaped so that there is a partially open intermediate position in which the axis of the latch stem and the axis of the needle shank define an angle which is preferably less than 90.degree..
2. Discussion of the Prior Art
Latch needles whose latches can be held in a partially open intermediate position by an associated spring element have in the past been used exclusively in hand knitting machines. When casting on loops, i.e. at the beginning of the knitting process or when forming further stitches, the partially open intermediate position of the latch makes it possible to unimpededly place the yarn into the needle hook. The partially open intermediate position avoids the necessity of using a brush-shaped needle opener or of initially opening all needle latches by hand. Both of these methods for opening the latch are connected with a considerable amount of work.
Attempts have been made to employ latch needles which have spring tensioned latches in knitting machines, and in particular in flat frame knitting machines. These needles would take the place of the previously employed normal latch needles having freely pivotally mounted latches. The reason for this is that the us of these normally employed latch needles (particularly when they are configured as stitch transfer needles) involves the danger that when the needle is retracted the latch does not properly pivot into its closed position and the stitch becomes caught at the tip of the open needle latch. The result of improper closing is that the yarn becomes snagged or split open. The reason this happens is because the stitch has been widened by the transfer spring of the transfer needle and the stitch is not pulled beneath the completely opened needle latch. This causes improper pivoting as the needle is retracted. Another problem that may happen is that the stitch slides over the open latch and is then caught in the needle hook. All of these possibilities result in faulty merchandise and the possibility of these flaws occurring increases when several yarns are knit simultaneously or when coarse natural yarns are processed.
Attempts to avoid this source of flaws by the use of latch needles having spring tensioned latches have been only partially successful. This is because a specific spring force is required to bring the latch from its closed or its completely open position into the partially open intermediate position and t arrest it there elastically. In prior art latch needles of this type, the force exerted on the latch by the spring element produces a great amount of friction for the latch which results in making the movement of the latch sluggish. Over time this affects the brush-shaped latch openers of the knitting machine in a manner such that the latches will no longer open reliably. At the same time, the end portion of the latch stem as well as the spring element experience wear from the constant friction at the spring element. The wear that occurs at the latch stem end causes the latch edges to become rounder after a longer period of operation and the wear of the spring element causes a reduction in the spring force. Thus the time period during which the pivoting movement of the latch is performed also becomes irregular in length because of the irregular friction conditions. These irregular conditions lead to an irregular appearance of the stitches in the knit fabric.
Such a latch needle that is intended for a hand knitting machine and that is unsuitable in principle for fast running flat frame knitting machines is disclosed in German Pat. No. 1,113,537. This needle has the latch slot located below the needle latch and is provided with a steel wire spring underneath the needle latch which is placed loosely into upwardly open steps at both ends of the latch slot so that the spring is undisplaceable in the longitudinal and transverse directions. Two flattened portions attached to the end portion of the latch stem cause the latch to be pressed back into a partially open intermediate position after each opening an closing movement in which position the axis of the needle latch and the axis of the needle shank form an angle of about 45.degree. with one another.
Such needles are very well suited for manually operated flat frame knitting machines where the above-mentioned drawbacks do not occur because, compared to a modern flat frame knitting machine, the knitting speed is extremely slow and the spring force of the spring inserted underneath the latch can be kept correspondingly low.
This also applies to another latch needle known in practice for hand knitting machines which has a spring tensioned latch. In this needle, the latch is pivoted back after every closing or opening movement into an approximately half-open intermediate position by means of a spring element configured as a circular, flat or square spring element. In this intermediate position, the axis of the needle latch and the axis of the needle shank form an angle of approximately 90.degree. with one another. One end of the spring element is braced into a groove made in the upper side of the needle shank and the groove opens into the latch slot. In the mentioned half-open intermediate position when the latch is to an angle of about 90.degree., the free end of the spring element, which extends into the latch slot, presses against the upper side of the latch stem where the latter is essentially linear. If the latch is pivoted by the newly formed stitch from this intermediate position back into its completely open position, the upper side of the latch stem presses the freely movable front portion of the spring element downward. After the stitch has slid onto the needle shank and has released the latch, the spring element is able to pivot the latch back into the intermediate position in which the latch is elastically locked by the free end of the spring element which has returned to its starting position.
When the needle is retracted and the stitch hanging on the needle shank moves in the direction of the needle hook, the stitch grips the latch in its intermediate position and pivots the stitch until the latch spoon rests on the hook as the needle continues to retract. Therefore the needle reaches its closed position. During this latch pivoting movement the free end of the spring element is in constant engagement with the latch stem. As the latch pivots, the free end of the spring element travels on a contact face of the end portion of the latch stem. It travels from the region of the latch bearing to the vicinity of the frontal face of the latch stem end portion. While this occurs the spring element is simultaneously pressed upwardly and is thus tensioned. After the stitch has been knitted the latch is released thus enabling the spring element which acts on the contact face of the latch stem to pivot the latch back into its intermediate position.
Attempts to use these latch needles which are intended exclusively for us in hand knitting machines in fast running flat frame knitting machines failed. They have failed because the structure of the knit fabric turned out to be so irregular that the merchandise could not be used. As far as it is known, the reason for this is the sluggish movement of the latch and the fluctuating tension forces to which the stitch is subjected to because of the irregular pivoting movements of the latch.